The goal of this project is to understand how a protein binds to single-stranded nucleic acids. Single-stranded nucleic acid-binding proteins play roles in key cellular processes such as DNA replication, recombination, repair, and control of RNA translation. If the ways in which proteins interact with single-stranded nucleic acids were understood in detail, then it might be possible to modify or correct the functions of human proteins such as replication protein A that are larger and more difficult to study. This would be important in the treatment of diseases due to deficiencies in the function of these proteins. We have obtained high-quality but small crystals of several complexes of gene 5 protein bound to single-stranded oligonucleotides. We hope that the determination of these structures will give insights into protein-ssDNA interactions that could not be obtained in any other way.